Electrodeposition of rhodium



SATE i PT ensure I ELECTRODEPOSITION or nnonrcm Sigmund Cohn, New York, N. Y., assignor to Baker 8: Company, Inc, Newark, N. .L, a corporation of New Jersey No Drawing. Original application March 31,

1931, Serial No. 526,786. Divided and this application November 9, 1935, Serial No. 49,029

13 Claims. (El. Zoo-1) This invention relates to a process for the invention will become apparent from the followelectrolytie deposition of rhodium and to a bath ing description and appended claims. for efieeting said deposition. The plating baths with which my process is -The precious metal, rhodium, according to operative, as stated above, comprise essentially 5 general practice is usually plated from strongly aqueous baths containing the precious metal 5 acid aqueous'baths containing said metal in the rhodium in the form of salts of weak acids. form of salts of strong mineral acids, the sulfate Any weak acid whether organic or in n c. bath being that most usually employed. This which forms a salt with the above metal may form of bath in order to be at all effective conbe employ d in connection with said metal for tains a high concentration of free sulfuric acid furnishing e e c on to he ec y e. 10 with the result, that during electrolysis a spray These Weak acids W comprise P b y c ds of this acid is given off thereby rendering the o an acidity of that of tartaric. o i c r c plating operation a, possible ur e f danger t benzoic, lactic and like organic acids and also the plater. In addition, aid a id spray may phosphoric and similar weak inorganic acids. 15 attack base metal objects adjacent to the plating Moreover, Said acids y b C m ed wi h Said tank. While this difiiculty could be overcome by metal either as simple salts or as complex salts providing a hood over the plating tank, the cost With alkali metals and ammonium as for incident. to this construction which must be acid example rhodium ammonium Oxalate, od um proof is a drawback to this process. Still ammonium r e. rhodium ammonium taranother drawback to the use of the above bath irate. rhodium ammonium n oate. rhodium resides in the corrosive action of-the free acid ammonium'lactate and the likeon base metal cathodes which must not there- A peculiarity of these baths which t y far re be i d r left standing in t t cilitates the deposition of the metal therefrom unless the current is on. Furthermore, the deand enhances the emflency 0f the electrolysis i posit obtained with this type of bath, is not, the feet that they may be p y wi h great always bright and coherent and in order t success either in an acid, neutral or alkaline tain any satisfactory deposit, very careful regcmditmn- The P p D f e bath, if it is ulation of the plating conditions must be to be alkaline. may be provided by a din a i t m certain amount of a weak or strong alkali to an si th t of t above precious metal and aqueous solution of the simple or double salts its salts is very high, it can be appreciated that of Said Precious metal. The aiiidity 0f the ath in view of the many objections to the use of the on the other h may be controlled by reguabove bath for plating these metals, the plating lated additions of free, Strong Weak acidsf d metal on commercial scale hasyhardly Obviously, this feature of my invention greatly bt i any degree of importance decreases the necessary skill required by the I have now found that the many objections to workmen operating the plating Processthe plating of aid precious t 1 in the No highly acid proof form of tank such for strongly a id bath above mentioned, can be Web instance, as fused silica, is necessary for concome and clear, brilliant deposits of said metal fining t plating soluti Since t corrosive obtained without a careful manipulation of the action of the same cpntmry to that of the $111- 40 plating process, by depositing said metal from photo bath, is small. Preferably,- the electrolyaqueous baths containing said metal. m the sis lS effected with an inert anode such as platiform of Salts with weak acids nulm ofi a: size sugflentttlo :IEVEIW high electrli); It is comm an b ca ress ance. e ca. 0 e o course may provide a g gzgg gg fi mf sfifigx any metal upon which it IS desired to plate, such deposits of rhodium without a careful and exas sflver gold platmum copper brass German pensive control of the plating operation and sllver' pewter and the like of course the I cathode, as in general plating should be clea without subjecting the operator to dangerou and smooth to facilitate the production 0 and disagreeable working conditions.

clear, dense, brilliant deposits. It s a further object of this invention to The concentration of the metal ions in soluvide a S mp e. eminent. relatively inexpensive tion may vary depending upon the conditions of process for electrolytically obtaining rhodium in temperature, electrical pressure andv cathode dense deposits of a high clarity andbrilliance. current density but need not be high to secure 55 other and further important objects of this good deposits. As a general rule, the anode cur 55 rent density is not of great importance but should be less than that 01' the cathode.

It is also not necessary with the baths of my invention to agitate the solution during plating or provide any other means to efiect depolarization of the electrodes, although a more even plate may be obtained if this is done.

The following example will serve to more fully illustrate the nature of my invention, but it should be borne in mind that my process is not limited to the specific conditions recited therein.

An aqueous solution of a salt of rhodium with a weak acid such' as rhodium oxalate, citrate, tartrate, benzoate, lactate, phosphate or the like or of a double salt of rhodium such as rhodium ammonium oxalate, rhodium ammonium citrate, rhodium ammonium benzoate or the like containing about 1 gram of rhodium per liter of solution is electrolyzed with a platinum anode and a smooth copper cathode which it is desired to plate at a voltage of about 4 volts and a cathodic current density of about 2 amperes per sq. inch. The electrolyte is maintained at a temperature of between 60" and 90 C. during the electrolysis. In this way dense, brilliant deposits of rhodium are obtained. 0! course, the usual D. C. current is used.

As stated above, the electrolyte may be acid, neutral or alkaline which conditions may be obtained by the use of the proper amount of a suitable acid or alkali. Generally an alkaline electrolyte is preferable. If, however, an acid bath is used, it is obvious that the acidity will not be made so high as to cause deposition of hydrogen to the exclusion of the metal. Likewise, excessive alkalinity should be avoided. These are however obvious details which will be varied at the option of the skilled plater under diiierent desired conditions of plating.

' It can thus be seen that I have provided a novel and highly efiicient process for obtaining dense, brilliant deposits of rhodium.

Various details of my process may of course be varied and I therefore do not intend to be limited in the scope of my invention except as necessitated by the prior art.

This application is filed as a division of my application for Electrodeposition of rhodium, Ser. No. 526,786, filed March 31, 1931.

What I claim is:

1. A process of depositing an adherent coating or layer of rhodium which comprises passing a D. C. current through an aqueous bath containing a rhodium lactate compound.

2. A process of depositing an adherent layer or coating of rhodium which comprises passing a D. C. current through a solution containing rhodium ammonium lactate.

3. A process of depositing an adherent layer or coating of rhodium which comprises passing a D. C. current through an aqueous alkaline bath containing a rhodium lactate compound.

4. A process of depositing an adherent layer or coating of rhodium which comprises passing a D. C. current through an aqueous alkaline bath containing rhodium ammonium lactate.

5. A process 01' electroplating rhodium which comprises passing a D. C. current at about 4 volts and a cathode current density of about 2. amperes per sq. inch through a rhodium lactate solution maintained at a temperature of about 60 to 90 C. I

6. A process of electrodepositing rhodium which comprises passing a D. C. current of about 4 volts at a cathodic current density of 2 amperes per sq. inch from a platinum anode through an alkaline rhodium ammonium lactate solution containing about 1 gram of rhodium per liter of solution.

7. An electrolyte for depositing rhodium which contains a rhodium lactate compound.

8. An electrolyte for electrodepositing coatings oi, rhodium which comprises an alkaline aqueous solution of rhodium lactate.

9. An electrolyte for depositing rhodium which contains rhodium ammonium lactate.

10. An electrolyte for electrodepositing coatings of rhodium. which comprises an alkaline aqueous solution of rhodium ammonium lactate.

11. A process for plating rhodium which comprises passing a direct current through an aqueous bath containing rhodium combined with an organic acid selected from the group consisting of tartaric, oxalic, citric, lactic and benzoic acids.

12. A process for plating a brilliant and dense layer of rhodium, which comprises passing a D. C. current through an aqueous bath containing rhodium, said rhodium being combined with an organic acid selected from the group consisting of tartaric, oxalic, citric, lactic, and benzoic acids, and maintaining the temperature between about 60 to 90 C. during the plating operation.

13. A process for plating a brilliant and dense layer of rhodium, which comprises passing a D. C. current through an aqueous bath containing rhodium, said rhodium being in the form of a complex compound with an organic acid selected from the group consisting of tartaric, oxalic, citric, lactic and benzoic acids, and a cation selected from the class consisting of the alkali metals and ammonium, and maintaining the temperature of the bath between about 60 to 90 C. during theplating operation.

SIGMUND COHN. 

